Liquid impermeable nonwoven sheet for absorbent article

ABSTRACT

A liquid impermeable sheet comprising a melt blown non woven fabric and an absorbent article using liquid impermeable sheet are provided. The melt blown non woven fabric comprises ultra fine fibers of thermoplastic polymer spun by a melt blowing method, and the fiber diameter is 10 μm or less. The melt blown non woven fabric satisfies the following Formulas (A): 2≦W/D 2 ≦200 and (B): 0.05≦d≦0.2 where W is basis weight (g/m 2 ), D is fiber diameter (μtm) and d is apparent density of the non woven fabric (g/cc), and thus, the fabric is excellent in feeling, flexibility and air permeability, while it keeps its liquid impermeability.

TECHNICAL FILED

[0001] This invention relates to a liquid impermeable sheet and anabsorbent article using the same. Such absorbent articles includemedical and sanitary materials such as disposable diapers and sanitarynapkins. More specifically, this invention relates to a liquidimpermeable sheet and an absorbent article comprising the liquidimpermeable sheet that is excellent in air permeability and feelingwhile keeping the desired liquid impermeability.

BACKGROUND ART

[0002] Absorbent articles such as disposable diapers and sanitarynapkins for medical and sanitary materials have been used to absorb bodyfluid like urine and blood and to prevent them from leaking. For thispurpose, such an absorbent article comprises at least a liquid absorbentlayer for absorbing and holding body fluid such as urine and blood, aliquid permeable surface cover that made of a non-woven fabric, a wovenfabric, a knitted fabric etc. and that is provided at the skin side ofthe article, and a liquid impermeable back sheet that is provided at theback side in order to prevent the absorbed body fluid from leakingoutside. Also, such an absorbent article usually comprises waterrepellent side sheets of a non-woven fabric or the like provided on bothsides of the absorbent article in addition to the back sheet in order toprevent the liquid such as the absorbed body fluid from leaking when theposition of the absorbent article is displaced from a predeterminedposition for wear by the movement of the body or when the wearer lies onhis side. (In disposable diapers or the like, the side sheet is oftengathered, and therefore it is called side gathers or a leg cuff. Indisposable diapers, the side sheets are provided in such a position thatthey surround and hold the groin or the thighs when the disposablediaper is worn). Also, in disposable diapers, a water repellent roundsheet of a non-woven fabric or the like is further provided on the skinsides of the portion covering the abdominal region and the portioncovering the upper hips at the opposite side so as to prevent the liquidsuch as the absorbed body fluid from leaking outside the absorbentarticle on the abdominal region or the upper hips as the wearer moves,for example, falls down, lies down, or turns his body. Furthermore, insome disposable diapers, band-like waist gathers or the like areprovided on the waist position skin side, and these also comprises awater repellent sheet of a non-woven fabric or the like.

[0003] Several kinds of liquid absorbent layers comprising cellulosefibers such as fluff pulp, highly-absorbing polymer and, if necessary, amixture of synthetic fibers are used.

[0004] In general, liquid impermeable sheets are used for back sheets ofsuch absorbent articles since comparatively good liquid impermeabilityis required for back sheets. Water repellent sheets used for sidesheets, round sheets and waist gathers, and have less waterimpermeability compared to the back sheets.

[0005] Thermoplastic films are used for the conventional back sheets ofabsorbent articles. The thermoplastic films are formed with countlessmicropores in order to prevent the inside of the film from gettingsticky in wearing and for air permeability. In some cases, the film iscombined with a non-woven fabric to improve the appearance and feelingof the film and also to improve the strength. Non-woven fabrics providedwith water repellency and some other properties are used for sidesheets, round sheets and waist gathers.

[0006] As mentioned above, liquid impermeable sheets and water repellentsheets are often used for absorbent article components.

[0007] Thermoplastic films having air permeability are used generallyfor back sheets of absorbent articles. However, the conventional backsheets are still unsatisfactory in providing two opposite properties,namely, liquid impermeability and air permeability. Thermoplastic filmsare not sufficient in air permeability though they provide good liquidimpermeability. Water repellant non-woven fabric is used for sidesheets, round sheets and waist gathers. However, it would be morepreferable if the liquid impermeability could be improved withoutsacrificing air permeability.

[0008] In Japanese Patent No. 2533253 (Japanese Patent ApplicationTokkai-Hei 4-226658), a liquid impermeable baffle layer is providedbetween the back sheet of plastic films and an absorbent so that acloth-like touch is provided while leakage is prevented. However, thearticle will be heavy due to its complicated configuration.

[0009] Japanese Patent Application Tokkai-Hei 6-14949 discloses animpermeable sheet provided between an absorbent and a plastic film, butthe function is still unsatisfactory.

[0010] This invention aims to provide a liquid impermeable sheet withgood air permeability and feeling while keeping its liquidimpermeability, and an absorbent article using the same. Another aim ofthis invention is to provide a liquid impermeable sheet for an absorbentarticle with excellent strength as well as the above properties and anabsorbent article using the same.

DISCLOSURE OF THE INVENTION

[0011] In order to achieve the above-mentioned objects, a liquidimpermeable sheet for an absorbent article of this invention comprises amelt blown non-woven fabric comprising ultra fine fibers ofthermoplastic polymer whose diameter is 10 μm at most, and the ultrafine fiber is spun by a melt blowing method. The melt blown non-wovenfabric satisfies the following Formulas A and B.

2≦W/D ²≦200  (A)

0.05≦d≦0.2  (B)

[0012] W: basis weight (g/m²)

[0013] D: fiber diameter (μm)

[0014] d: apparent density of the non-woven fabric (g/cc)

[0015] It is preferable in the sheet that a fiber non-woven fabriccomprising a thermoplastic polymer is further laminated.

[0016] It is preferable in the sheet that the melt blown non-wovenfabric comprises thermoplastic ultra fine conjugated fibers having adiameter of 10 μm at most, where a low melting point polymer and a highmelting point polymer are conjugated and the melting point differencebetween the polymers is at least 15° C.

[0017] It is preferable in the sheet that the melt blown non-wovenfabric comprises thermoplastic ultra fine combined fibers having fiberdiameter of 10 μm at most, where a low melting point polymer and a highmelting point polymer are combined and the melting point differencebetween the polymers is at least 15° C.

[0018] It is preferable in the sheet that the liquid impermeable sheetis at least one sheet selected from the group consisting of a backsheet, a side sheet, a round sheet and a waist gather for an absorbentarticle.

[0019] It is preferable in the sheet that the melt blown non-wovenfabric comprises at least one polymer selected from the group consistingof polyolefin polymer and polyester polymer.

[0020] It is preferable in the sheet that the fiber composing the meltblown non-woven fabric is at least one fiber selected from the groupconsisting of single fiber of a single composition, conjugated fiberformed by conjugating a low melting point polymer and a high meltingpoint polymer, and combined fiber formed by combining a low meltingpoint polymer and a high melting point polymer.

[0021] It is preferable in the sheet that the average fiber diameter ofthe melt blown fabric as 0.1-9 μm.

[0022] It is preferable in the sheet that the basis weight of the meltblown non-woven fabric is 4-50 g/m².

[0023] It is preferable in the sheet that the thermoplastic fibernon-woven fabric comprises filament and/or staple fiber.

[0024] It is preferable in the sheet that the thermoplastic non-wovenfabric comprises two-composition conjugated fiber formed by conjugatinga low melting point polymer and a high melting point polymer.

[0025] It is preferable in the sheet that the difference of the meltingpoints between the high melting point polymer and the low melting pointpolymer is at least 15° C.

[0026] It is preferable in the sheet that the fiber is at least oneconjugated fiber selected from the group consisting of sheath-core typefiber, eccentric sheath-core type fiber, parallel type fiber, multilayertype fiber and sea-island type fiber.

[0027] It is preferable in the sheet that the polymer compositioncomposing the conjugated fiber is at least one polymer selected from thegroup consisting of polyolefins, polyesters and polyamides.

[0028] It is preferable in the sheet that the fineness of the singlefiber composing the non-woven fabric is 0.5-10 d/f.

[0029] It is preferable in the sheet that the length of the staple fibercomposing the non-woven fabric is 3-51 mm.

[0030] It is preferable in the sheet that the staple fiber composing thenon-woven fabric is at least one fiber selected from the groupconsisting of crimped fiber and uncrimped fiber.

[0031] It is preferable in the sheet that the cross section of the fiberhas at least one shape selected from the group consisting of circular,modified, and hollow.

[0032] It is preferable in the sheet that the melt blown non-wovenfabric and a fiber non-woven fabric for lamination are laminated byusing at least one bonding method selected from the group consisting ofa heat bonding by embossed rollers, ultrasonic welding, a hot air cyclebonding using hot air blow at a temperature within the range between themelting points of a high melting point polymer and a low melting pointpolymer, and a hot melt bonding using a hot melt polymer.

[0033] An absorbent article of this invention comprises, for at leastone of its portions, the liquid impermeable sheet of this invention.

[0034] A non-woven fabric of this invention, composing a liquidimpermeable sheet for an absorbent article, is a thermoplastic ultrafine fiber non-woven fabric comprising fibers spun in a melt blowingmethod, and the fiber diameter is 10 μm or less. The non-woven fabricsatisfies the Formulas A and B, and thus, a liquid impermeable sheetcomprising the non-woven fabric has good air permeability whilemaintaining liquid impermeability, and excellent feeling andflexibility. Such sheets are preferably used for absorbent articles.

[0035] Furthermore, a laminate comprising the melt blown non-wovenfabric and another thermoplastic fiber non-woven fabric is preferablyused in the embodiments of this invention. As a result, a liquidimpermeable sheet that has good non-woven fabric strength and goodfeeling can be provided, and such sheets are preferably used forabsorbent articles.

[0036] The melt blown non-woven fabric of this invention preferablycomprises thermoplastic ultra fine conjugated fiber made of a lowmelting point polymer and a high melting point polymer, the differenceof the melting points between the polymers being at least 15° C., andthe fiber diameter being 10 μm at most. As a result, liquid impermeablesheets with less fuzz, which are preferably used for absorbent articles,are provided.

[0037] The melt blown non-woven fabric of this invention preferablycomprises thermoplastic ultra fine fibers formed by combining a lowmelting point polymer and a high melting point polymer, the differenceof the melting points between the polymers being at least 15° C., andthe fiber diameter being 10,μm at most. As a result, liquid impermeablesheets with less fuzz, which are preferably used for absorbent articles,are provided.

[0038] A thermoplastic fiber non-woven fabric to be laminated on themelt blown non-woven fabric is preferably a filament non-woven fabric inthis invention. As a result, liquid impermeable sheets comprising thenon-woven fabric have less fuzz, and thus, the sheets have good strengthand are preferably used for absorbent articles.

[0039] The liquid impermeable sheet in the preferable embodiments ofthis invention is at least one selected from the group consisting of aback sheet, a side sheet, a round sheet and a waist gather, so that goodair permeability and liquid impermeability are effectively used, andabsorbent articles having excellent feeling and flexibility can bemanufactured.

[0040] An absorbent article comprising the liquid impermeable sheet ofthis invention does not cause a problem of body fluid leakage from thearticle to the outside, while air permeability and feeling of the sameabsorbent article are good.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 is a plan view showing one example of a disposable diaperpartially using a liquid impermeable sheet of this invention, inunwrapped form, as seen from the skin side.

[0042]FIG. 2 is a schematic cross sectional end view taken on line X-X′of FIG. 1.

[0043]FIG. 3 is a schematic cross sectional end view taken on line Y-Y′of FIG. 1.

[0044]FIG. 4 is a plan view showing one example of a sanitary napkinpartially using a liquid impermeable sheet of this invention, inunwrapped form, as seen from the skin side.

[0045]FIG. 5 is a schematic cross sectional end view taken on line X-X′of FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

[0046] A non-woven fabric used for a liquid impermeable sheet for anabsorbent article of this invention is a non-woven fabric spun by a meltblowing method.

[0047] A melt blown non-woven fabric is produced by the following steps,though the details are omitted as this fabric is well known. Athermoplastic polymer is melted and extruded to be a fiber from a meltblowing spinneret. At the same time, a hot gas is injected at a highspeed from a slit formed around the spinning orifice in order to blowthe gas to the extruded fiber melted polymer flow. The fiber flow isdeposited on a scavenger such as collecting endless net conveyor toobtain an ultra fine fiber web. The web is processed to be a non-wovenfabric by heat-sealing if necessary. (see Japanese Patent ApplicationTokkai Hei 1-156561; Industrial and Engineering Chemistry No. 8, Vol.48, 1956, p.1342-1346; Basic and Application of Non-woven Fabric (issuedon Aug. 25, 1993) p.119-127 etc., edited by the Non-woven FabricResearch Society in Japan Fiber Machine Academy (incorporatedassociation).

[0048] In this melt blowing method, fiber is produced in the followingprocess: extruding melted fiber from a spinneret; injecting a hot, highspeed gas to blow the flow of the fiber melted polymer in order to drawthe extruded fiber melted polymer and to provide a ultra fine fiberflow. The fiber is drawn in melted condition so generally it is notoriented due to the drawing. Therefore, the non-woven fabric comprisesfibers that are substantially undrawn. The non-woven fabric typicallycomprises ultra fine staple fibers since the melted fibers are torn offby the hot, high speed air flow.

[0049] Air is generally used for the hot, high speed gas, however, anyother gases such as steam can be used as long as they do not react withand deteriorate the melted polymer. The gas temperature ranges from 300to 400° C., though it depends on the kinds of the melt-extrudedpolymers, and the gas pressure ranges, for example, 1-5 kg/cm². Thecondition, however, is not limited to these ranges.

[0050] Polyolefin polymers and polyester polymers are preferably usedfor the polymers to be the thermoplastic fibers used in the melt blownnon-woven fabric. The polyolefin polymers include polypropylene, highdensity polyethylene, linear low density polyethylene,ethylene/propylene binary copolymer, and ethylene/butene 1/propyleneternary copolymer. The polyester polymers include polyethyleneterephthalate and polybutylene terephthalate. Pigments, flame retarders,deodorants, antistatic agents and antioxidants can be added to thethermoplastic fibers in an amount such that the additives do notdeteriorate the effects of the invention.

[0051] The fibers composing the melt blown non-woven fabric can beselected from the group consisting of single fiber comprising a singlecomposition, conjugated fiber formed by conjugating a low melting pointpolymer and a high melting point polymer, and combined fiber formed bycombining a low melting point polymer and a high melting point polymer.In a non-woven fabric comprising conjugated or combined fibers, thedifference of the melting points between a high melting point polymerand a low melting point polymer is preferably at least 15° C. Otherwise,the high melting point polymer will also be softened or melted andeasily lose its fiber shape when a non-woven fabric is produced by thehot air cycle bonding method. Such a non-woven fabric will look like afilm and its feeling will deteriorate. A non-woven fabric comprisingconjugated or combined fibers is preferable since it can provide aliquid impermeable sheet with less fuzz for an absorbent article. Anarticle comprising the conjugated or combined fibers is preferred to anarticle comprising single fiber having a single composition, since thefibers can be heat-bonded to each other easily without using additivesand thus the strength of the non-woven fabric can be improved.

[0052] The average fiber diameter of the melt blown fabric of thisinvention is preferably 10 μm or less, more preferably, 0.1-9 μm. It isfurther preferable that the diameter range is 0.2-8 μm. Fiber with adiameter from 10 to 0.1 μm is preferred since it provides excellentfeeling, and it is easily produced at a low cost.

[0053] The apparent density (d(g/cc)) of the melt blown non-woven fabricfor this invention is 0.05≦d≦0.2. When the apparent density (d) of themelt blown non-woven fabric is less than 0.05, the texture of the fabricbecomes ununiform. As a result, the liquid impermeability required forthe liquid impermeable sheet for the absorbent article cannot bemaintained even if the basis weight is high, and liquid will be leaked.When the apparent density (d) exceeds 0.2, the feeling and appearancewill deteriorate due to the bad air permeability and compression,although sufficient liquid impermeability is maintained. Such a fabricis improper for a liquid impermeable sheet for an absorbent article.

[0054] The basis weight of the melt blown non-woven fabric for thisinvention is preferably 4-50g/m², more preferably, 4-30 g/m². When thebasis weight is too small, the liquid impermeability will deteriorate,and the cost of providing finer fibers for keeping liquid impermeabilitywill rise. When the basis weight is too big, the fabric will be thickand the feeling will deteriorate, and such a fabric is not proper for aliquid impermeable sheet for an absorbent article. A non-woven fabrichaving the above range of basis weight is preferably used to avoid theabove-identified problems.

[0055] The melt blown non-woven fabric for this invention should meetthe requirement: 2≦W/D²≦200 when W: basis weight (g/m²), D: fiberdiameter (μm).

[0056] This formula indicates that a thin non-woven fabric basis weightcan be used if the fibers composing the melt blown non-woven fabric arefine, while the basis weight should be thick if the fiber diameter isbig. No melt blown non-woven fabric with sufficient air permeability andliquid impermeability can be obtained when the fabric does not meet theabove formula even if the apparent density (d) of the fabric is withinthe range of 0.05≦d≦0.2.

[0057] A melt blown non-woven fabric for this invention can be usedwithout processing after it is spun and scavenged. Or it can becompressed by using smooth rollers in order to control its apparentdensity. The smooth rollers can be heated to a degree such that the meltblown non-woven fabric will not be like a film, and unheated smoothrollers also can be used.

[0058] Some other methods can be used for bonding the fibers: embossroll heat bonding, ultrasonic welding and hot air cycle bonding (amethod to use hot air in a temperature range between the melting pointsof two kinds of polymers).

[0059] The melt blown non-woven fabric for this invention can be used bylaminating with other kinds of thermoplastic fiber non-woven fabrics inorder to improve strength and touch, and to prevent fuzz. Thethermoplastic fiber fabrics can comprise staple fibers or filaments.

[0060] The thermoplastic fiber non-woven fabric can be a cardednon-woven fabric or an air laid non-woven fabric, etc., if the fabriccomprises staple fibers. The staple fibers composing the staple fibernon-woven fabric can contain a single composition, or they can beconjugated fibers comprising at least two compositions, for example,three or four compositions. Considering cost, however, a two-compositionconjugated fiber comprising a high melting point polymer and a lowmelting point polymer will be sufficient for most general purposes.

[0061] Preferable polymer compositions that can be used for the abovethermoplastic non-woven fabric comprising staple fibers are, forexample, polyolefin polymers, polyester polymers and polyamide polymers.The polyolefin polymers include polypropylene, high densitypolyethylene, linear low density polyethylene, ethylene/propylene binarycopolymer, and ethylene/butene-1/propylene ternary copolymer. Thepolyester polymers include polyethylene terephthalate and polybutyleneterephthalate. The polyamide polymers include nylon 6 and nylon 66.Pigments, flame retarders, deodorants, antistatic agents andantioxidants can be added to the thermoplastic fiber in the range suchthat the additives do not deteriorate the effects of the invention.

[0062] In a non-woven fabric comprising conjugated staple fiber, thedifference of the melting points between a high melting point polymerand a low melting point polymer is preferably at least 15° C. For theconjugated staple fiber, sheath-core type fiber, eccentric sheath-coretype fiber, parallel type fiber, multilayer type fiber and sea-islandtype fiber can be used.

[0063] The cross section of the fibers for the staple fiber non-wovenfabric used for a laminating layer can be circular or various modified-shapes such as polygonal, flat and stellate. The fibers can be hollow.Or the non-woven fabric can be produced by combining these fibers.

[0064] Though the fineness of the fiber composing the staple fibernon-woven fabric for lamination is not specifically limited, it ispreferably 0.5-10 d/f. If the fineness is too small, a needle of ahopper feeder will merely thread when the staple fibers are opened. As aresult, an uneven staple fiber non-woven fabric with neps will beproduced. On the other hand, the staple fiber will be stiff if thefineness is too big. In this case, flexibility of the staple fibernon-woven fabric will deteriorate. The length of the staple fiber ispreferably 3-51 mm, since a non-woven fabric balanced in bulkiness,openness and homogeneity will be obtained.

[0065] Moreover, crimped or uncrimped staple fibers can be used.Specifically, crimped fibers such as spiral type, zigzag type andU-shape type are preferable due to the good bulkiness.

[0066] Several methods can be used to laminate the melt blown non-wovenfabric and the staple fiber non-woven fabric for lamination, forinstance, heat-bonding by using embossed rollers, ultrasonic welding,hot air cycle bonding with hot air blown at a temperature in the rangebetween a low melting point and a high melting point of two kinds ofpolymers, and a hot melt method using hot melt polymer.

[0067] By using a staple fiber non-woven fabric to laminate with the hotblown non-woven fabric of this invention, a liquid impermeable sheet foran absorbent article can be provided. The sheet is not deteriorated inair permeability and liquid impermeability, is improved in feeling, andis excellent in bulkiness and flexibility.

[0068] When a thermoplastic fiber non-woven fabric laminated with a meltblown non-woven fabric of this invention comprises filaments, thefilaments can contain a single composition, or it can be a conjugatedfiber comprising at least two compositions, for example, three or fourcompositions. Considering cost, however, a two-composition conjugatedfiber comprising a high melting point polymer and a low melting pointpolymer will be sufficient for most general purposes.

[0069] Preferable polymer compositions that can be used for the abovethermoplastic non-woven fabric comprising filaments are, for example,polyolefin polymers, polyester polymers and polyamide polymers. Thepolyolefin polymers include polypropylene, high density polyethylene,linear low density polyethylene, ethylene/propylene binary copolymer,and ethylene/butene-1/propylene ternary copolymer. The polyesterpolymers include polyethylene terephthalate and polybutyleneterephthalate. The polyamide polymers include nylon 6 and nylon 66.Pigments, flame retarders, deodorants, antistatic agents andantioxidants can be added to the thermoplastic fiber in a range suchthat the additives do not deteriorate the effects of the invention.

[0070] When conjugated fibers are used for laminating the filamentnon-woven fabric, the difference of the melting points between a highmelting point polymer and a low melting point polymer is preferably atleast 15° C.

[0071] For the conjugated filaments, sheath-core type, eccentricsheath-core type, parallel type, multilayer type and sea-island type canbe used.

[0072] The cross section of the filaments can be circular or variousmodified shapes such as polygonal, flat, and stellate. The fiber can behollow. Or the non-woven fabric can be produced by combining thesefibers.

[0073] A “spun bond” method is preferably used for producing thefilament non-woven fabric for lamination in this invention, though thereis no limitation.

[0074] The spun bond method is as follows:

[0075] providing polymer in an extruder;

[0076] melt-spinning the polymer by using a spinneret;

[0077] introducing a group of fibers spewed from the spinneret into anair sucker for drawing to obtain filaments;

[0078] charging the group of filaments from the air sucker by a propercharging device such as a corona discharging device; and

[0079] opening the group of filaments by passing the filaments through apair of vibrating flaps or by impacting them on a proper reflectingboard etc.; and

[0080] depositing the opened group of filaments as a filament fleece ona collecting endless net conveyor provided with a sucking device on thebackside.

[0081] It is possible to use a non-woven fabric that is provided byopening converged tows obtained by a typical melt-spinning, instead ofthe spun bond method.

[0082] For producing this filament non-woven fabric, conjugated fiberscomprising two kinds of polymers whose melting points are different byat least 15° C. can be used. When using conjugated fibers, polymers ofthe compositions are introduced to respective extruders and melt-spun byusing a conjugating spinneret.

[0083] It is also possible that the filament non-woven fabric is formedby combining low melting point polymer filaments and high melting pointpolymer filaments, where the difference in the melting points is atleast 15° C.

[0084] Though there is no specific limitation, the fineness of thefilament non-woven fabric for lamination in this invention is preferably0.5-10 d/f. Too small fineness will raise cost, and too big finenesswill deteriorate the feeling.

[0085] Several methods can be used to laminate the melt blown non-wovenfabric and the filament non-woven fabric for lamination, for instance,heat-bonding by using embossed rollers, ultrasonic welding, hot aircycle bonding where hot air is blown at a temperature in the rangebetween a low melting point and a high melting point of two kinds ofpolymers, and a hot melt method using hot melt polymer.

[0086] If a filament non-woven fabric is used for laminating with a meltblown non-woven fabric of this invention, fuzz is reduced while the airpermeability and liquid impermeability do not deteriorate, and strengthis improved while keeping good flexibility and feeling. As a result, aspecifically preferable liquid impermeable sheet for an absorbentarticle can be provided.

[0087] A typical example of the liquid impermeable sheet of thisinvention is explained below by referring to the drawings, in which thesheet is used for parts of absorbent articles. It should be noted thatthe shown configurations of the absorbent articles are just someexamples, and the drawings do not limit the configuration of theabsorbent article. The liquid impermeable sheet of this invention can beused for parts of various absorbent articles, where liquid impermeablesheets or water repellent sheets are used, but the whole configurationof the absorbent articles is not specifically limited.

[0088]FIG. 1 is a plan view of one example of a disposable diaper ofthis invention in unwrapped form, as seen from the skin side. FIG. 2 isa schematic cross-sectional end view taken on line X-X′ of FIG. 1. FIG.3 is a schematic cross-sectional end view taken on line Y-Y′ of FIG. 1.

[0089] In FIGS. 1-3, 1 denotes a liquid absorbent layer to absorb andhold body fluid. The liquid absorbent layer comprises cellulose fibersuch as fluff pulp, resin of highly water-absorbing polymer, and a mixedsynthetic fiber as required, though the materials are not limitedthereto. The liquid absorbent layer 1 can be wrapped with tissue paperas required. Numeral 2 denotes a liquid permeable surface cover providedat the surface (the skin side), comprising a non-woven fabric, a wovenfabric or a knitted fabric etc. Numeral 3 denotes a back sheet thatshould be liquid impermeable. A round sheet 4 is not always necessary.In FIGS. 2-3, the round sheet 4 is provided between the liquid absorbentlayer 1 and the back sheet 3. Numerals 5 and 5′ denote side sheetsprovided on both sides of the absorbent article in order to preventliquid such as absorbed body fluid from leaking when the position of theabsorbent article is displaced from a predetermined position for wear bythe movement of the body or when the wearer lies on his side asmentioned above. In disposable diapers or the like, the side sheets areoften gathered, and therefore they are called side gathers or a legcuff. In disposable diapers, the side sheets are provided in such aposition that they surround and hold the groin or the thighs. Band-likewaist gathers may be provided on the waist position skin sides asdenoted by 7 and 7′ in FIG. 1, though they are not shown in FIGS. 2 and3. Suitable parts of these members are bonded so that they do not drop,though such description is omitted in the drawings. In conventionalproducts, liquid impermeable sheets have been used for back sheets, andwater-repellent sheets have been used for side sheets, round sheets andwaist gathers. The liquid impermeable sheet of this invention canprovide disposable diapers, a kind of absorbent article, which have goodair permeability and feeling while keeping liquid impermeability, byusing the present sheets for at least one part selected from the groupconsisting of back sheets, side sheets, round sheets and waist gathersof conventional absorbent articles. It is specifically effective to usethe sheet for a back sheet of an absorbent article since it covers acomparatively large surface, and it has a liquid impermeabilitysufficient for a back sheet and good air permeability and feeling.

[0090]FIG. 4 shows a plan view of an example of a sanitary napkin seenfrom the skin side; and FIG 5 shows a schematic cross-section end viewtaken on line X-X′ of this figure. Numeral 1 denotes a liquid absorbentlayer. Numeral 2 denotes a liquid permeable front cover located on thesurface side of the liquid absorbent layer (the side to contact theskin), and the cover is selected from the group consisting of a meshsheet, a non-woven fabric, a woven fabric and a knitted fabric. 3denotes a back sheet requiring liquid impermeability; 5 and 5 ′ denoteside sheets. Suitable parts of these members are bonded so that they donot drop, though such description is omitted in the drawings. The liquidimpermeable sheet of this invention can provide sanitary napkins, a kindof absorbent article, which have good air permeability and feeling whilekeeping liquid impermeability, by using the sheets for at least one partselected from the group consisting of a back sheet and a side sheet etc.It is specifically effective to use the sheet for a back sheet of anabsorbent article such as a sanitary napkin since it covers acomparatively large surface, and it has a liquid impermeabilitysufficient for a back sheet and good air permeability and feeling.

EXAMPLES

[0091] This invention will be specifically explained by referring tofollowing Examples, however, this invention is not limited to the scopeof these Examples.

[0092] The physical property values in the Examples were measured in thefollowing way.

Fiber Diameter

[0093] Ten pieces approximately 1 cm square were cut out from a meltblown non-woven fabric, though there was no specific limitation as tothe location. The pieces were photographed by using a scanning electronmicroscope (SEM) with a magnifying power of 100-5000. Average value ofthe fiber diameter (unit: μm) was obtained by measuring the diameter oftotal 100 fibers (10 in each of the ten sample pieces).

Non-woven Fabric Strength

[0094] A non-woven fabric with 5 cm width was prepared. Longitudinal andvertical breaking strength (kg/5 cm) of the fabric were measured byusing a tensile strength tester (AUTOGRAPH AG-500D by ShimadzuCorporation). The average value from five samples was substituted in thefollowing formula and calculated.

(Longitudinal breaking strength×Vertical breaking strength)^(½)

[0095] The data were divided by (basis weight×5 cm) so that non-wovenfabric strength (unit: kg/cm(g/m²)) was obtained.

Apparent Density of Non-woven Fabric

[0096] Weight per 1 m² of a melt blown non-woven fabric was measured,and the thickness of the melt blown non-woven fabric was measured byusing a SEM, in order to calculate weight per 1 cc (unit: g/cc).

Air Permeability

[0097] The average value was calculated from five samples by using anair permeability tester made by Toyoseiki Seisakusho CO., LTD., based onJISL 1004, 1018 (unit: cc/cm²/second).

Hydraulic Resistance

[0098] An average value was obtained from five samples by using ahydraulic resistance measuring instrument made by Toyoseiki SeisakushoCO., LTD. The unit was mm.

Example 1

[0099] A web of a melt blown non-woven fabric was obtained by thefollowing steps:

[0100] melting polypropylene at 330° C.;

[0101] providing the polypropylene to a spinneret having circular crosssection heated at 300° C. in order to melt spin;

[0102] blowing the polymer extruded from the spinneret with a hot, hightemperature air flow (temperature: 350° C.; gas pressure: 3.2 kg/cm²);depositing a web of a melt blown non-woven fabric on a collectingendless net conveyor; and

[0103] passing the web in a compression processor comprising smoothrollers that are heated at 120° C.

[0104] The web was passed though compressed rollers of a point bondprocessor comprising embossed and smooth rollers and being heated at130° C., so that the fibers were partially heat-bonded with each other.

[0105] The melt blown non-woven fabric had a fiber diameter (D) of 1.5μm, and a basis weight (W) of 27 g/m². The apparent density (d) of thenon-woven fabric (abbreviated as non-woven fabric density in the Tables)was 0.09 g/cc, and the value in the Formula A (Formula A value inTable 1) was 12.

[0106] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability while keeping its hydraulicresistance. The condition is shown in Table 1, and the result is shownin Table 2.

[0107] The liquid impermeable sheet was used for back sheets of variousabsorbent articles shown in FIGS. 1-5, including disposable diapers andsanitary napkins, for wearer evaluation. As a result, there was noleakage of body fluid to the outside of the absorbent articles, whileboth air permeability and feeling were highly evaluated.

Example 2

[0108] A melt blown non-woven fabric was obtained in the same way as inExample 1, except that the fiber diameter (D) was 1.0 μm and the FormulaA value was 27.

[0109] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability while keeping its hydraulicresistance. The condition is shown in Table 1, and the result is shownin Table 2.

[0110] The liquid impermeable sheet was used for back sheets of variousabsorbent articles shown in FIGS. 1-5, including disposable diapers andsanitary napkins, for wearer evaluation. As a result, there was noleakage of body fluid to the outside of the absorbent articles, whileboth air permeability and feeling were highly evaluated.

Example 3

[0111] A melt blown non-woven fabric was obtained in the same way as inExample 1, except that the density (d) was 0.08 g/cc, the basis weight(W) was 10 g/m² and the Formula A value was 4.4.

[0112] A melt blown web whose fiber diameter (D) was 1.0 μm and basisweight (W) was 10 g/m² was obtained in the same way as Example 1.

[0113] Another thermoplastic fiber non-woven fabric for lamination wasobtained in the following steps:

[0114] melting polypropylene at 300° C. and melting polyethylene at 220°C.;

[0115] providing the polypropylene and polyethylene from respectiveextruders to a sheath-core type conjugating spinneret heated at 280° C.;

[0116] melt-spinning the composition so that the polypropylene composesthe core and the polyethylene composes the sheath;

[0117] passing the core-sheath type conjugated fibers through an airsucker by using a spun bond method and taking it in at 2500 m/min.;

[0118] opening the fibers by forcibly charging using a charging device;

[0119] forming a filament fleece deposited on a collecting conveyor; and

[0120] laminating the filament fleece on the melt blown non-woven fabricweb.

[0121] The laminate was passed through compressed rollers of a pointbond processor having embossed and smooth rollers heated at 128° C., sothat the fibers were partially heat-bonded.

[0122] The part of the laminated melt blown non-woven fabric had anapparent density (d) of 0.08 g/cc, and the Formula A value was 4.4.

[0123] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability while keeping its hydraulicresistance. The non-woven fabric strength was also improved bylaminating a filament non-woven fabric. The condition is shown in Table1, and the result is shown in Table 2.

[0124] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, there was no leakage of body fluid to theoutside of the absorbent articles, while both air permeability andfeeling were highly evaluated.

Example 4

[0125] A web of a melt blown non-woven fabric with fiber diameter (D) of1.5 μm and basis weight (W) of 10 g/m² was obtained by the followingsteps:

[0126] melting polyethylene at 220° C. and melting polypropylene at 330°C.;

[0127] providing the polyethylene and polypropylene from respectiveextruders to a combination type spinneret heated at 300° C. formelt-spinning;

[0128] blowing the polymer extruded from the spinneret with a hot, highspeed air flow of 350° C., 3 kg/cm² (gas pressure);

[0129] depositing a web of a melt blown non-woven fabric on a collectingendless net conveyor; and

[0130] compressing the web in the same way as Example 1.

[0131] A thermoplastic non-woven fabric for lamination was obtained inthe same way as Example 3.

[0132] The filament fleece was laminated on the above melt blownnon-woven fabric, and the-fibers of the laminate were partiallyheat-bonded to each other by passing the laminate through compressedrollers of a point bond processor comprising embossed and smooth rollersheated at 126° C.

[0133] The apparent density (d) of the melt blown non-woven fabric was0.8/cc and Formula A value was 4.4 after the lamination.

[0134] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability with less fuzz, while keepingits hydraulic resistance. The non-woven fabric strength was alsoimproved by laminating filament non-woven fabric. The condition is shownin Table 1, and the result is shown in Table 2.

[0135] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, there was no leakage of body fluid to theoutside of the absorbent articles, while both air permeability andfeeling were highly evaluated.

Example 5

[0136] A web of a melt blown non-woven fabric fiber with diameter (D) of1.5 μm and basis weight (W) of 10 g/m² was obtained by the followingsteps:

[0137] melting propylene-ethylene-butene-1 ternary copolymer(copolymerization ratio of ethylene was 2.5 wt % and butene-1 was 4.5 wt%, and this ternary copolymer is indicated as COPP in Table 1) at 250°C. and melting polypropylene at 330° C.;

[0138] providing the polymers from respective extruders to a sheath-coretype conjugating spinneret heated at 300° C. for melt-spinning in orderto obtain sheath-core type conjugated fibers (the sheath is the ternarycopolymer and the core is polypropylene);

[0139] blowing the polymer extruded from the spinneret with a hot, highspeed air flow of 350° C., 3 kg/cm² (gas pressure);

[0140] depositing a web of a melt blown non-woven fabric on a collectingendless net conveyor; and

[0141] compressing the web in the same way as Example 1.

[0142] A filament fleece of conjugated fibers for thermoplastic fibernon-woven fabric to be laminated was prepared in the same way as Example3 except that polyethylene (a low melting point composition) wasreplaced by propylene-ethylene-butene-1 ternary copolymer extruded at240° C.

[0143] Next, the filament fleece was laminated on the melt blownnon-woven fabric, and the fibers of the laminate were partially bondedto each other by passing the laminate through compressed rollers of apoint bond processor comprising embossed and smooth rollers heated at128° C.

[0144] The apparent density (d) of the melt blown non-woven fabric was0.08/cc and Formula A value was 4.4 after the lamination.

[0145] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability with less fuzz, whilemaintaining its hydraulic resistance. The non-woven fabric strength wasalso improved by laminating filament non-woven fabric. The condition isshown in Table 1, and the result is shown in Table 2.

[0146] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, there was no leakage of body fluid to theoutside of the absorbent articles, while both air permeability andfeeling were highly evaluated.

Example 6

[0147] A web of a melt blown non-woven fabric with fiber diameter (D) of1.5 μm and basis weight (W) of 10 g/m² was obtained by the followingsteps:

[0148] melting polyethylene at 220° C. and melting polypropylene at 330°C.;

[0149] providing the polyethylene and polypropylene from respectiveextruders to a parallel type spinneret heated at 300° C. formelt-spinning;

[0150] blowing the polymer extruded from the spinneret with a hot, highspeed air flow of 350° C., 3.2 kg/cm² (gas pressure);

[0151] depositing a web of a melt blown non-woven fabric on a collectingendless net conveyor; and

[0152] compressing the web in the same way as Example 1.

[0153] Fibers of 2.5 d/f were prepared for a thermoplastic fibernon-woven fabric used for lamination by the following steps:

[0154] melting polypropylene at 300° C. and melting polyethylene at 220°C.;

[0155] providing the polypropylene and polyethylene from respectiveextruders to an eccentric sheath-core type conjugating spinneret heatedat 280° C. for melt-spinning;

[0156] winding the spun eccentric sheath-core type fibers (sheathcomposition is polyethylene and core composition is polypropylene)around a bobbin;

[0157] drawing the fibers to four times the original length by using100° C. drawing rollers; and

[0158] providing the fibers with zigzag crimps by using a stuffer boxtype crimper. The fibers were cut to be 38 mm long, being passed througha carding. machine, so that a web of a staple fiber non-woven fabric wasprepared.

[0159] The staple fiber non-woven fabric web was laminated on the meltblown non-woven fabric, and the fibers of the laminate were partiallybonded to each other by passing the laminate through compressed rollersof a point bond processor comprising embossed and smooth rollers heatedat 126° C.

[0160] The apparent density (d) of the melt blown non-woven fabric was0.08 g/cc and Formula A value was 4.4 after the lamination.

[0161] The melt blown non-woven fabric was proper for a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability while keeping its hydraulicresistance. The non-woven fabric strength was also improved bylaminating a staple fiber non-woven fabric. The condition is shown inTable 1, and the result is shown in Table 2.

[0162] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, there was no leakage of body fluid to theoutside of the absorbent articles, while both air permeability andfeeling were highly evaluated.

Example 7

[0163] A melt blown non-woven fabric web was obtained in the same way asExample 5, except that a combination type spinneret was used. In otherwords, a melt blown non-woven fabric web comprising combined fibers ofpolypropylene ultra fine fibers and propylene-ethylene-butene-1 ternarycopolymer ultra fine fibers was obtained.

[0164] An eccentric sheath-core type conjugated filament fleece (sheathcomposition is propylene-ethylene-butene-1 ternary copolymer and corecomposition is polypropylene) for a thermoplastic fiber non-woven fabricused for lamination was obtained in the same way as Example 5 exceptthat an eccentric sheath-core type spinneret was used.

[0165] The filament fleece was laminated on the melt blown non-wovenfabric, and the fibers of the laminate were partially bonded to eachother by passing the laminate through compressed rollers of a point bondprocessor comprising embossed and smooth rollers heated at 128° C.

[0166] The apparent density (d) of the melt blown non-woven fabric was0.08/cc and Formula A value was 4.4 after the lamination.

[0167] The melt blown non-woven fabric was proper to a liquidimpermeable sheet for an absorbent article since it was excellent infeeling, flexibility and air permeability with less fuzz while keepingits hydraulic resistance. The non-woven fabric strength was alsoimproved by a filament non-woven fabric. The condition is shown in Table1, and the result is shown in Table 2.

[0168] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, there was no leakage of body fluid to theoutside of the absorbent articles, while both air permeability andfeeling were highly evaluated.

Comparative Example 1

[0169] A melt blown non-woven fabric web was prepared in the same way asExample 1 except that the basis weight (W) was 20 g/m² and compressingtreatment was not carried out.

[0170] The fibers of the melt blown non-woven fabric web were partiallybonded to each other by passing the laminate through compressed rollersof a point bond processor comprising embossed and smooth rollers heatedat 130° C.

[0171] The apparent density (d) of the melt blown non-woven fabric wasonly 0.03 g/cc though Formula A value was 9.

[0172] The melt blown laminated non-woven fabric had good airpermeability, however, it was not appropriate for a liquid impermeablesheet used in an absorbent article, as it did not keep its hydraulicresistance. The condition is shown in Table 1, and the result is shownin Table 2.

[0173] The liquid impermeable sheet was used for back sheets of variousabsorbent articles shown in FIGS. 1-5, including disposable diapers andsanitary napkins, for wearer evaluation. As a result, the evaluation wasbad due to body fluid leakage to the outside of the absorbent articles,although the air permeability and feeling were good.

Comparative Example 2

[0174] A melt blown non-woven fabric was produced in the same way asExample 7 except that the basis weight of the non-woven fabric was 4g/m², and a filament fleece for a thermoplastic fiber non-woven fabricto be laminated on the melt blown non-woven fabric web was produced inthe same way as Example 7.

[0175] The filament fleece was laminated on the melt blown non-wovenfabric, and the fibers of the laminate were partially bonded to eachother by passing the laminate through compressed rollers of a point bondprocessor comprising embossed and smooth rollers heated at 128° C.

[0176] The apparent density (d) of the melt blown non-woven fabric was0.09 g/cc, but Formula A value was 1.8 after the lamination.

[0177] The melt blow laminated non-woven fabric had good airpermeability, however, it was not appropriate for a liquid impermeablesheet used in an absorbent article, as it did not keep its hydraulicresistance. The condition is shown in Table 1, and the result is shownin Table 2.

[0178] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, the evaluation was bad due to body fluidleakage to the outside of the absorbent articles, although the airpermeability and feeling were good.

Comparative Example 3

[0179] A web of a melt blown non-woven fabric with 2.0 μm of fiberdiameter (D) and 7 g/m² of basis weight (W) was obtained by thefollowing steps:

[0180] melting polyethylene at 220° C. and melting polypropylene at 330°C.;

[0181] providing the polyethylene and polypropylene from respectiveextruders to a parallel type conjugating spinneret heated at 300° C. formelt-spinning;

[0182] blowing the polymer extruded from the spinneret with a hot, highspeed air flow of 350° C., 2.8 kg/cm² (gas pressure);

[0183] depositing a web of a melt blown non-woven fabric on a collectingendless net conveyor; and

[0184] compressing the web in the same way as Example 1.

[0185] Fibers of 2.5 d/f were prepared for a thermoplastic fibernon-woven fabric to be-laminated, by the following steps:

[0186] melting polypropylene at 300° C. and melting polyethylene at 220°C.;

[0187] providing the polypropylene and polyethylene from respectiveextruders to an eccentric sheath-core type conjugating spinneret heatedat 280° C. for melt-spinning;

[0188] winding the spun eccentric sheath-core type conjugated fibers(sheath composition is polyethylene and core composition ispolypropylene) around a bobbin;

[0189] drawing the fibers to four times the original length by using100° C. drawing rollers; and

[0190] providing the fibers with zigzag crimps by a stuffer box typecrimper. The fibers were cut to be 38 mm long, being passed through acarding machine, and webs of a staple fiber non-woven fabric wereprepared.

[0191] The staple fiber non-woven fabric web was laminated on the meltblown non-woven fabric, and the fibers of the laminate were partiallybonded to each other by passing the laminate through compressed rollersof a point bond processor comprising embossed and smooth rollers heatedat 126° C.

[0192] The apparent density (d) of the melt blown non-woven fabric was0.1 g/cc while Formula A value was 1.8 after the lamination.

[0193] The melt blow laminated non-woven fabric had good airpermeability, however, it was not appropriate for a liquid impermeablesheet used in an absorbent article, as it did not keep its hydraulicresistance. The condition is shown in Table 1, and the result is shownin Table 2.

[0194] The liquid impermeable sheet comprising the laminated non-wovenfabric was used for back sheets of various absorbent articles shown inFIGS. 1-5, including disposable diapers and sanitary napkins, for wearerevaluation. As a result, the evaluation was bad due to body fluidleakage to the outside of the absorbent articles, although the airpermeability and feeling were good. TABLE 1 Melt blown non-woven fabricNon-woven fabric for lamination Fiber Fabric Basis Resin Formula ResinDiameter Density Weight Compo- A Compo- (μm) (g/cc) (g/m²) Type sitionValue Fiber type Type sition Example 1 1.5 0.09 27 Single PP 12 — — —Example 2 1.0 0.09 27 Single PP 27 — — — Example 3 1.5 0.08 10 Single PP4.4 Filament Sheath-core PE/PP Example 4 1.5 0.08 10 Combined PE/PP 4.4Filament Sheath-core PE/PP Example 5 1.5 0.08 10 Sheath-core COPP/PP 4.4Filament Sheath-core COPP/PP Example 6 1.6 0.08 10 Parallel PE/PP 4.4Staple Eccentric PE/PP Fiber sheath-core Example 7 1.5 0.08 10 CombinedCOPP/PP 4.4 Filament Eccentric COPP/PP sheath-core Comparative 1.5 0.0320 Single PP 8.9 — — — Example 1 Comparative 1.5 0.09 4 Combined COPP/PP1.8 Filament Eccentric COPP/PP Example 2 sheath-core Comparative 2.0 0.17 Parallel PE/PP 1.8 Staple Eccentric PE/PP Example 3 Fiber sheath-core

[0195] TABLE 2 Non-woven fabric physical value Non-woven Basis AirHydraulic Fabric Weight Impermeability Resistance strength (g/m²)(cc/cm² · sec.) (mm) kg/cm(g/m²) Example 1 27  9 350 0.007 Example 2 2710 350 0.007 Example 3 30 50 280 0.042 Example 4 28 50 280 0.042 Example5 28 50 280 0.043 Example 6 28 50 280 0.048 Example 7 28 50 280 0.042Comparative 20 90 150 — Example 1 Comparative 26 80 120 — Example 2Comparative 28 90 110 — Example 3

1. A liquid impermeable sheet for an absorbent article, comprising amelt blown non-woven fabric comprising ultra fine fibers ofthermoplastic polymer, the polymer being spun by a melt blowing methodand the fiber diameter being 10 μm at most, the melt blown non-wovenfabric satisfying the following Formulas A and B, 2≦W/D²≦200  (A)19.05≦d≦0.2  (B) where W is basis weight (g/m²), D is fiberdiameter (μm), and d is apparent density of the non-woven fabric (g/cc).2. The liquid impermeable sheet for an absorbent article according toclaim 1, further comprising a fiber non-woven fabric of thermoplasticpolymer laminated on the melt blown non-woven fabric.
 3. The liquidimpermeable sheet for an absorbent article according to claim 1, whereinthe melt blown non-woven fabric comprises thermoplastic ultra thinconjugated fibers whose diameter is 10 μm at most, and the fiber isprovided by conjugating a low melting point polymer and a high meltingpoint polymer, the difference in the melting points between the polymersbeing at least 15° C.
 4. The liquid impermeable sheet for an absorbentarticle according to claim 1, wherein the melt blown non-woven fabric isa combined material of thermoplastic ultra fine fibers whose diameter is10,μm at most, and the fibers comprise a low melting point polymer and ahigh melting point polymer, the difference in the melting points betweenthe polymers being at least 15° C.
 5. The liquid impermeable sheet foran absorbent article according to claim 1, wherein the liquidimpermeable sheet is formed as a sheet selected from the groupconsisting of a back sheet, a side sheet, a round sheet and a waistgather for an absorbent article.
 6. The liquid impermeable sheet for anabsorbent article according to claim 1, wherein the melt blown non-wovenfabric comprises at least one polymer selected from the group consistingof a polyolefin polymer and a polyester polymer.
 7. The liquidimpermeable sheet for an absorbent article according to claim 1, whereinthe fibers composing the melt blown non-woven fabric are at least onefiber selected from the group consisting of single fiber, fiber formedby conjugating a low melting point polymer and a high melting pointpolymer, and fiber formed by combining a low melting point polymer and ahigh melting point polymer.
 8. The liquid impermeable sheet for anabsorbent article according to claim 1, wherein the average fiberdiameter of the melt blown non-woven fabric is 0.1-9 μm.
 9. The liquidimpermeable sheet for an absorbent article according to claim 1, whereinthe basis weight of the melt blown non-woven fabric is 4-50 g/m². 10.The liquid impermeable sheet for an absorbent article according to claim2, wherein the thermoplastic fiber non-woven fabric is a non-wovenfabric comprising at least one fiber selected from the group consistingof filament and staple fiber.
 11. The liquid impermeable sheet for anabsorbent article according to claim 10, wherein the thermoplastic fibernon-woven fabric comprises a two-composition conjugated fiber formed byconjugating a low melting point polymer and a high melting pointpolymer.
 12. The liquid impermeable sheet for an absorbent articleaccording to claim 11, wherein the difference in the melting pointsbetween the high melting point polymer and the low melting point polymeris at least 15° C.
 13. The liquid impermeable sheet for an absorbentarticle according to claim 11, wherein the conjugated fiber is at leastone fiber selected from the group consisting of sheath-core type fiber,eccentric sheath-core type fiber, parallel type fiber, multilayer typefiber and sea-island type fiber.
 14. The liquid impermeable sheet for anabsorbent article according to claim 11, wherein the polymer compositioncomposing the conjugated fiber is at least one polymer selected from thegroup consisting of polyolefins, polyesters and polyamides.
 15. Theliquid impermeable sheet for an absorbent article according to claim 10,wherein the fineness of the single fiber composing the non-woven fabricis 0.5-10 d/f.
 16. The liquid impermeable sheet for an absorbent articleaccording to claim 10, wherein the length of the staple fiber composingthe non-woven fabric is 3-51 mm.
 17. The liquid impermeable sheet for anabsorbent article according to claim 10, wherein the staple fibercomposing the non-woven fabric is at least one fiber selected from thegroup consisting of crimped fiber and uncrimped fiber.
 18. The liquidimpermeable sheet for an absorbent article according to claim 2, whereinthe cross section of the fiber is at least one shape selected from thegroup consisting of circular, modified, and hollow.
 19. The liquidimpermeable sheet for an absorbent article according to claim 2, whereinthe melt blown non-woven fabric and the fiber non-woven fabric forlamination are laminated by using at least one bonding method selectedfrom the group consisting of a heat bonding by embossed rollers, anultrasonic welding, a hot air cycle bonding using hot air blown at atemperature within the range between the melting points of the highmelting point polymer and the low melting point polymer, and a hot meltbonding using a hot melt polymer.
 20. An absorbent article comprisingthe liquid impermeable sheet according to claim 1.